1. Field of the Invention
The present invention relates to CNC controlled machines with continuous production control. Specifically, the invention relates to a CNC controlled glass cutting line including a glass table with a dynamic, continuous production control system.
2. Background Information
Glass cutting lines, including glass cutting tables, are well-known in the art, such as those sold by the assignee of the present invention, Billco Manufacturing, Inc. The central piece of equipment in the glass cutting line is the glass cutting table, examples of which are described in U.S. Pat. Nos. 5,791,971 and 6,463,762 and pending patent application Ser. No. 09/277,534, which are incorporated herein by reference. The glass cutting table is designed to cut generally rectangular glass sheets into a plurality of individual glass workpieces for subsequent manufacturing. The typical glass cutting line will also include a sheet feeding device upstream of the glass cutting table for feeding the glass sheets to be cut to the glass cutting table. The sheet feeding device may be in the form of an air float table to which individual glass sheets to be cut are fed, such as from a storage rack, and then aligned prior to forwarding to the glass cutting table. The typical glass cutting line will also include a sorting device downstream of the glass cutting table where the cut glass sheets are individually sorted by the specific glass workpieces into storage racks, generally called harp racks. A harp rack is provided with a number of slots, such as 100, for receiving the individual cut glass workpieces. The sorting device may be formed as an air float table with a plurality of adjacent harp racks.
Existing glass cutting lines typically utilize a production control system designed to minimize scrap. Currently, a specific cutting schedule for a production run, or single batch, is prepared in advance by the control system. The production run essentially corresponds to the number of harp racks and associated slots at the sorting station. Basically, existing optimization programs are used to determine the optimal cutting schedule for filling the slots of the harp racks with the desired glass workpieces. The cutting schedule essentially refers to the collection of layouts of the individual glass workpieces on all the glass sheets to be cut for the production run or batch. Following the production run, the filled harp racks can be moved to the next location in the manufacturing process. It is important to note that different harp racks may go to different assembly lines and, therefore, may have widely different product mixes, i.e., a different set of individual glass workpieces filling the different harp racks. At the end of the production run is the last sheet, which generally has the lowest yield (i.e., the highest scrap) because the glass workpieces formed from this “last sheet” do not fill up the sheet. Additionally, some control systems allow for recuts to be added to the last sheet to help minimize the yield loss of the entire production cycle. Recuts are duplicate workpieces to replace previous cut workpieces that may have been damaged, broken or otherwise unusable.
The existing systems are limited by several problems. First, each system is limited by the number of available slots in the available harp racks. In general, the greater the number of slots the greater the yield since the optimizing program will have a greater number of pieces to select from to maximize product yield. Second, the harp racks generally cannot be moved until the entire production run is completed, including the recuts at the end of the batch process. Third, the existing last sheet problem increases yield loss, even with recuts incorporated into the last sheet. Additionally, the existing system does not easily accommodate special pieces not accounted for in the production run. It is one object of the present invention to overcome these problems of the prior art optimization systems and provide an efficient, effective glass cutting line with dynamic production control.